Application of the high-accuracy universal polarimeter to magnetic and absorbing crystals

Abstract

In this paper we show that the high-accuracy universal polarimeter can be used to investigate the optical properties of (almost) any crystal through which light can be transmitted. The only extra condition is that the reciprocal linear birefringence (or the reciprocal linear dichroism) of the sample is large with respect to the other optical effects that are present. The sample is allowed to exhibit reciprocal linear birefringence and reciprocal circular birefringence. This is the situation for which the high-accuracy universal polarimeter was originally intended. We show, however, that reciprocal linear dichroism and reciprocal circular dichroism may also be present. The method can, therefore, be applied to (weakly) absorbing crystals. Furthermore, optical effects are taken into account that are related to the breaking of time-reversal symmetry. These are the non-reciprocal circular birefringence, non-reciprocal circular dichroism, non-reciprocal linear birefringence and non-reciprocal linear dichroism. This means that, under some conditions, each (weakly) absorbing, magnetic crystal can be investigated with the high-accuracy universal polarimeter. We derive a unified formula for the intensity change of the light that propagates through the polarimeter. This expression can be used to determine the (complex) eigenpolarizations of an arbitrary sample. Moreover, it is shown how this unified formula can be translated to a formula in terms of the different birefringent and dichroic optical effects. The relevant formula for a specific case can, therefore, be given directly. The method is demonstrated by means of measurements on samples of NiSO4.6H2O. This material shows reciprocal linear birefringence, reciprocal linear dichroism, reciprocal circular birefringence and reciprocal circular dichroism, simultaneously.